抽时间就得练练脑子，清醒清醒db.stu.aggregate([{$match:{age:{$gt:20}}},{$group:{_id:"$gender",人数:{$sum:1},年龄大于20姓名:{$push:"$name"}}}])
db.stu.aggregate([{$match:{age:{$gt:20}}},{$group:{_id:"$gender",人数:{$sum:1},年龄大于20姓名:{$push:"$name"}}}])
